Rubber compounding



Patented Dec. 15, 1942 RUBBER COMPOUNDING Theodore Adolph Bulifant,Hackensack, N. J., as

signor, by mesne assignments, to Allied Chemical & Dye Corporation, acorporation of New York No Drawing.

14 Claims.

This invention relates to improvements in the manufacture of rubberstock and more particularly to a novel process of compounding rubber andto a novel composition for use in such process.

In the manufacture of vulcanized rubber articles, it is customary to addcompounding materials to the rubber batch for softening the rubber tofacilitate milling, impart the desired working characteristics, e. g.molding and extrusion properties, and effect pigmentation of the rubberstock. Coke oven tar pitches possess advantageous rubber-softening andpigmentation properties and impart to the rubber desirable WOI'kingcharacteristics. It has been found,.however, that in some cases the useof coke oven tar pitches as rubber-compounding materials is subject tothe disadvantage that vulcanized rubber stocks in which such pitcheshave been incorporated have a tendency to develop a dirty, brownish orgreenish surface discoloration, known in the rubber trade as bloom,within a few weeks or months after vulcanization. The avoidance of bloomis of especial importance to the manufacturers and distributors ofrubber goods since it involves loss of sales and good will and entailsthe expense of replacing unsatisfactory articles. While the causes ofbloom are not fully understood, it is believed to be due in part atleast to migration to the surface of the stock of materials of limitedsolubility in rubber when other incompatible ingredients are present.Whatever may be the reason for bloom, it has been found that it isespecially likely to occur when vulcanized rubber articles have beenwrapped or packaged so as to prevent free circulation of air over thesurface of the rubber.

It is an object of this invention to provide a novel process ofcompounding rubber for the manufacture of rubber stock free fromobjectionable blooming tendencies. The invention also comprehends anovel rubber-compounding composition of matter for use as a rubbersoftener without imparting objectionable blooming tendencies to therubber stock.

In accordance with the invention, I incorporate in the rubber mix, pitchresidue resulting from distillation of water gas tar to soften therubber, facilitate working of the mix and to impart the desiredcharacteristics to the rubber stock. I preferably employ as thesoftening agent pitch residue of a softening point (ring and ball)falling within the range of 165 F. to 235 F. and a penetration of 25 C.,200 grams, and seconds Application December 20, 1938, Serial No. 246,851

of from 0 to 20, resulting from the distillation of heavy water gas tar.I have found that when water gas tar pitch softening agent is mixed withbatches of rubber stocks and the stocks milled, vulcanized and cured,the resultant vulcanized rubber may be stored indefinitely without de-Veloping objectionable bloom.

The invention also comprehends blending with the water gas tar pitchprior to incorporating it in the rubber mix, a plasticizing andlubricating agent which softens the pitch, reduces its brittleness andtendency to scatter during milling and lubricates the pitch to render itless tacky, thereby preventing sticking of the rubber to the mill rollsand improving the processing properties of the mix. Materials havingsoftening and lubricating properties and which form a homogeneousmixture when blended with water gas tar pitch in the desired propertionsare in general suitable for accomplishing the desired results. A largenumber of such plasticizing and lubricating agents havebeen found toimpart the desired properties to water gas tar pitch, in particularhigh-molecular-weight aliphatic materials, especially fatty oils, highmolecular weight fatty acids and their derivatives, and asphalticmaterials, particularly natural asphalt. v r

The water gas tar pitch employed may be produced by distilling heavyWater gas tar, i. e. water gas tar of specific gravity above 1.1,specific viscosity (Engler) above 6 for 0.0. at 40 C., and having a freecarbon content in excess 01' 1% until a pitch residue having a softeningpoint preferably falling within the range of from F. to F. is produced.While I prefer to employ pitch resulting from the distillation'oi' heavywater gas tar, pitches derived from other water gas tar may also beutilized with advantage I'or compounding rubber. Water gas tar, as iswell known in the water gas industry, is obtained in the cooling andwashing OI carburetted water gas usually made by blasting a fuel bedwith an and alternately passing steam through the hot fuel bed, theresultant Water gas being enriched by the addition thereto of Oil vaporsproduced by the cracking of petroleum oil including residues anddlstlllates of petroleum oil. Heavy Water gas tar results when heavyoils such as Bunker C for oil or residuums are used to enrich the watergas; light water gas tars usually result when gas oil is used to enrichthe water gas. Water gas tar differs in its chemical and physicalproperties from coke oven tars.

As illustrative of the use of water gas tar pitch for compounding rubberin accordance with the invention, the following examples of theincorporation of the pitch in rubber mixes are given:

Example I A suitable composition for the, manufacture of black rubbersoling stock is as follows, parts being by weight:

The above ingredients were assembled and milledin the customary manner,the milled prodnot was then cured for twelve minutes at 316 F.

' Example II A product was prepared in the same manner and with similarmaterials except that instead of the water gas tar pitch of Example Ithere were employed 20 parts by weight of heavy water gas tar pitch of asoftening point (ring and ball) of 203 F., a benzol insoluble content of24.6 per 'cent, and penetrations (200 grams, seconds) as follows: at 25C.l; at 40 C.16; at 461 (L-41; at 50 C.-85 at 60 C.--223; at 70 C.-355+.

. Example III A product was prepared in the same manner and with s'imilar fnaterials as in the foregoing examples except that instead of theheavy water gas tar pitch of such examples, there were employed 20 partsby weight of heavy Water gas tar pitch of a softening point (ring andball) of 210 F a benzoliinsoluble content of 29.3 per cent, andpenetrations (200 grams, 5 seconds) as followsz'at 25 C.-0.5+; at 40C.5; at 46.1 (l-20; at 50 'C.-3'8; at 60 C.84'; at 70 (3. 252.

'Eficamp'le IV A product was-prepared in the same manner as in theforegoing examples using similar materials except that there wereemployed 20 parts of. heavy water gas tar pitch of a-softening point(ringand ball) of 234 F., a benzol insoluble content of 32.5 per cent,and penetrations (200 grams, 5 seconds) as follows: at 25 C.0.5; at 40C.1; at 461 C.7; at 50 C.19; at 60 C.-34; at 70 C.72.

The curedrubber stocks of Examples I to IV inclusive exhibited notendency to bloom after storage for eighteen weeks. The stocks weresubjectedto plasticity, abrasion, tear, flexing, tentile, and hardnesstests. The results of these tests showed the stocks to possesssatisfactory properties; for example, the results of the tensile andhardness tests on 't'he'stocks (A); before aging and (B) after aging forfourteen days at 70 C. are as follows:

The following ingredients were mixed in a manner similar to Example Iand cured for thirty minutes at a temperature of 281 F. for themanufacture of black rubber compounds:

A B O D Parts Parts Parts Parts by by by L 'ght L weigh/i Smoked sheetrubber 100 100 100 Heavy water gas tar itch of a softening point (ringand ball of 210 F I... 25 50 Coke oven tar, pitch of a softening point(ring and ball) of 184 F .1 25 I 50 Carbon black 50* 50 50 Zinc oxide 1010 l0 Antioxidant (phenyl-beta-naphthylamine) l 1 1 l l Stearic acid 4 44 '4 Sulfur 3 3 3 3 Mercaptobenzothiazole (captax) l 1 1 1 Thevulcanized stocks were inspected for bloom after aging for 5 and 10weeks; the results of the observations are tabulated below:

A B O D After 5 weeks None Green... None"; Green; After 10 weeks do dodo Do.

black. Since carbon black is a relatively inex pensive ingredient,vulcanized rubber stocks of similar hardness may be manufactured moreeconomically using water gas tar pitch than coke oven tar pitch as acompounding mate rial.

tory compounding material for rubber, I have found the processingproperties of the rubber mix may be improved by adding to the pitchprior to mixing it with the rubber aplastioi zi-ng and lubricating agentwhich reduces the brittleness of the pitch with consequent reduction ofthe tendency of the pitch to 'flyfrom the rubber mix during milling andwhich has a lubricating action preventing'sticking of themix'tothe'millrolls; in general many vegetable oils and fats;

While water gas tar pitch alone is-a satisfac animal oils and greases,mineraloils and waxes, aliphatic acids and derivatives thereof, andasphalts impart improved processing properties to the pitch. I prefer toemploy high-molecular-weight aliphatic materials, especially fatty oilssuch as palm oil and corn oil, high molecular weight fatty acids such asstearic acid and corn oil fatty acid, and aliphatic acid derivativessuch as oleic alcohol and diglycol laurate alone or in conjunction withasphalt for plasticizing and lubricating the pitch in accordance withthe invention. The proportions in which the plasticizing and lubricatingagents employed may be added to the pitch may vary to a considerableextent; I prefer to employ from 5 to per cent, based on the weight ofthe water gas tar pitch, although from 2 to 20 per cent may be employedin some cases.

As illustrative of blends of water gas tarpitch and plasticizing andlubricating agents, the following examples are given, parts being byweight: Water gas tar pitch 98 parts, palm oil 2 parts; water gas tarpitch 95 parts, palm oil 5 parts; water gas tar pitch 90 parts, palm oil10 parts; water gas tar pitch 85 parts, palm oil parts; water gas tarpitch 80 parts, palm oil parts; water gas tar pitch 92.5 parts, palm oil2.5 parts, Bermudez asphalt 5 parts. Water gas tar pitch may also beblended with the following plastici'zing and lubricating agents,preferably in proportions of from 90 to 95 parts of the pitch to 5 to 10parts of the plasticizing and lubricating agent: corn oil, corn oilfatty acid, steariic acid, oleic alcohol and 'diglycol laurate.

The ingredients of each example were melted together and after stirringuntil the materials are well mixed, were allowed to cool. The resultantcompositions exhibited the properties of a homogeneous blend.

The blends of water gas tar pitch and the plasticizing and lubricatingagents possess less susceptibility to temperature changes and mix morereadily with rubber than water gas tar pitch alone. Furthermore, rubbermixes in which the blends are incorporated mill smoothly and uniformlywithout objectionable flying of the pitch or sticking of the mix to themill rolls.

From the above description of the invention, it willbe appreciated thatvulcanized rubber stocks compounded with water gas tar pitch softener inaccordance with the invention are not subject to the objectionabletendencies to develop bloom which characterizes stocks compounded withcoke oven tar pitch. Furthermore, the milling properties of water gastar pitch are improved by blending therewith minor proportions ofplasticizing and lubricating agents which reduce the brittleness of thepitch and prevent sticking of the rubber mix to the mixing rolls.

While the preferred ratio of heavy water gas tar pitch to rubberhydrocarbon (as illustrated in the above examples) lies in the range 1:4to 1:2. this pitch in some formulas may show the advantages described inas small a ratio as 1:5. and in other formulations may be used in aneven greater ratio than 1:2.

Softening points, penetrations, tensile breaking points, elongation andhardnness given herein were determined in accordance with testsprescribed by the American Society for Testing Materials. Specificviscosities, i. e. the ratios obtained by dividing the time of flow ofthe material by the time of flow of an equal volume of water at 25.0 C.were determined by TestB-lll Viscosity, Engler), sheets #25 and #26, inMethods of Testing Coal Tar Products, copyrighted'by The BarrettCompany, 1931.-

I claim:

1. In a process of compounding rubber to form a non-blooming rubber, thesteps comprising mixing rubber with the pitch residue resulting from thedistillation of water gas tar, the ratio of the pitch to the rubberhydrocarbon falling within the range 1:5 to 1:2, said pitch having asoftening point (ring and ball) fallingwithin the range of about from165 F. to 235 F., and milling the mixture.

2. In a process of compounding rubber. to form a non-blooming rubber,the steps comprising blending pitch residue resulting from the distilrlation of water gas tar with asphalt for the pitch, mixing the blend ofpitch and asphalt with rubber, in such quantity that the ratio of thepitch to the rubber hydrocarbon falls within the range 1:5 to 1:2, andmilling the mixture 3. In a process of compounding rubber to form anon-blooming rubber the steps comprising blending pitch residueresulting from distillation of water gas tar with a minor proportion ofhigh-molecular-weight aliphatic plasticizing and -lubricating agent forthe pitch, mixing the re-'- sultant blend with rubber, in such quantitythat the ratio of the pitch to the rubber hydrocarbon falls within therange 1:5 to 1:2, and milling the mixture.

4. In a process of producing non-blooming vulcanized rubber the stepscomprising blending water gas tar pitch of a softening point (ring andball) of from 165 F. to 235 F. with a minor proportion ofhigh-molecular-weight vegetable fatty oil plasticizing and lubricatingagent, mixing the resultant blend with rubber, in such quantity that theratio of the pitch to the rubber hydrocarbon falls within the range 1:5to 1:2,

and milling the mixture.

5. In a process of producing non-blooming vulcanized rubber stock thesteps comprising blending Water gas tar pitch of a softening point (ringand ball) of from F. to 235 F. with from 2 to 20 per cent of palm oil,mixing the resultant blend with rubber, in such quantity that the ratioof the pitch to the rubber hydrocarbon falls within the range 1:5 to1:2, and milling the mixture.

6. In a process of compounding rubber to form a non-blooming rubber, thesteps comprising blending water gas tar pitch with a minor proportion ofpalm 011 and Bermudez asphalt, mixing the resultant blend with rubber,in such quantity that the ratio of the pitch to the rubber hydrocarbonfalls within the range 1:5 to 1:2, and milling the mixture.

'7. A composition for addition to rubber stock to facilitate milling andimpart improved working characteristics, comprising a major proportionof water gas tar pitch and a minor proportion of high molecular-weightaliphatic plasticizing and lubricating agent, obtained by melting thewater gas tar pitch, blending the plasticizing and lubricating agentwith the melted pitch and cooling to produce a uniformly blendedproduct.

8. In a process of producing non-blooming vulcanized rubber the stepscomprising incorporating water gas tar pitch and a vulcanizing agent inrubber, the ratio of the pitch to the rubber hydrocarbon falling withinthe range 1:4 to 1:2 and vulcanizing th mixture.

9. A composition for addition to rubber stock to facilitate. milling andimpart improved Work! ing characteristics, comprising a major proportionof' water gas tar pitch and a minor proportion of high-.molecular-weightaliphatic plasticizing and lubricating agent for the pitch. 10.. Acomposition for addition to rubber. stock to faciiltate milling andimpart improved, work'- ing characteristics, comprising from about 80.to

98 per cent water gas tar pitch. and from about 2. to 20 per cent ofvegetable. fatty oil blended therewith.

11. A solid. non-blooming vulcanized rubber product containing reacted.vulcanizing material and a blend of water gas tar pitch with ahighmolecular weight aliphatic plasticizing and lubricating agent, theratio of the pitch to the rubber hydrocarbon falling Within. the rangeof 1:5- to 1:22

12. A solid non-blooming vulcanized rubber product containing reactedvuicanizing. material andwater gas tar pitch, the. ratio of the pitch togreater. than 1- part by weight of the pitch to a each. 2 parts byweight of the rubber, and vul- V canizing the resultant rubbercompound.-

14. A, solid resilient non-bloomingvulcanized rubber product containingreacted vulcanizing material and. water gas tar pitch; the amount ofwater gas tarpitch being sufficient to, soften and facilitate working ofthe rubber prior to vulcani zation but not greater than 1-1 part--byweight of the-pitch for each 2 parts by Weight of the? rubberconstituent of the product.

' THEODORE ADOLPH. BUIJFANT. f H

